I have recently been getting a number of DNS lookup time-outs under Firefox. For those unfamiliar with the term, a Domain Name Server is what is used to convert a site name into a numeric address (e.g. http://www.cameralabs.com 72.3.225.30).

The solution described in thread (http://www.cameralabs.com/forum/viewtopic.php?t=1210) didn't work so I did a little digging in Firefox's About:config entries page. It turns out that by default Firefox only caches 20 DNS entries and if your URL isn't in the cache then it asks the operating system to resolve the name. For me that involves the Windows DNS cache (which seems to be a variable feast) and then finally a trip to my ISP's name servers.

Firefox's DNS cache default of 20 might have been good a few years ago but if, like me, you make regular use of RSS feeds which update often or you are just a heavy browser { insert your own jokes here } then you can very quickly fill that cache. And no, you don't have to visit 20 sites to do this as a huge number of sites host content from third parties and for every one of those third party links a DNS lookup has to occur unless the address has been pre-translated.

Anyway, as usual with Firefox, the cache limit parameter can be changed. The relevant entry is network.dnsCacheEntries and its description and instructions on how to change it are described here. This entry has to be added to the config and I have set a value of 256 which seems to be working nicely. If you want to be even more adventurous the setting network.dnsCacheExpiration also seems to have a rather low default of 60 seconds. It's described here and I've set this to 120 for now.

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Yes, it helped me, though it may also have helped hide an underlying problem with my ISP's own name servers.

I raised a tech support issue with them and as part of the troubleshooting they suggested a couple of open DNS (servers) to try. That really solved my problem as I haven't had a single DNS time-out since. I'm now waiting for my ISP to admit/fix the problem on a more permanent basis as I feel slightly more vulnerable using third party DNS.

EDIT: While my ISP has now rebooted its DNS server I think I'll stick with OpenDNS for now, with my ISP DNS addresses added as third and fourth choices. Not sure whether it's just the new DNS servers or my tweaking of the Firefox and Windows caches but my browsing suddenly seems much more responsive which is a pretty neat trick on a 6Mbps ADSL line. On reflection, this improvement is likely down to my ISP's recent poor DNS server response times so I wouldn't recommend trying OpenDNS unless you think you may have a problem.